Numerous devices utilizing electronic and optical systems are known for controlling the movement of an object through a predetermined path, the object being, for example, a robot arm, a cutting device or a machine tool. The basic problem with these prior art devices is that they have a limited tracking accuracy of about 1 part per 5,000, that is in a volume 10 feet by 10 feet by 20 feet, the accuracy is only about 0.05 inch.
Thus, these prior art control devices are unable to provide an extremely high degree of accuracy.
Examples of prior art devices relating to measuring the location of objects are disclosed in the following U.S. Pat. Nos. 3,471,239 to Woodson; 3,658,427 to DeCou; 3,790,284 to Baldwin; 4,261,107 to Coleman et al; 4,436,417 to Hutchin; and 4,457,625 to Greenleaf et al, the disclosures of which are hereby incorporated by reference.